Nuclear Receptors as Therapeutic Targets in Liver Disease: Are We There Yet?

Liver macrophage-associated inflammation correlates with SIV burden and is substantially reduced following cART

Liver disease is a leading contributor to morbidity and mortality during HIV infection, despite the use of combination antiretroviral therapy (cART). The precise mechanisms of liver disease during HIV infection are poorly understood partially due to the difficulty in obtaining human liver samples as well as the presence of confounding factors (e.g. hepatitis co-infection, alcohol use). Utilizing the simian immunodeficiency virus (SIV) macaque model, a controlled study was conducted to evaluate the factors associated with liver inflammation and the impact of cART. We observed an increase in hepatic macrophages during untreated SIV infection that was associated with a number of inflammatory and fibrosis mediators (TNFα, CCL3, TGFβ). Moreover, an upregulation in the macrophage chemoattractant factor CCL2 was detected in the livers of SIV-infected macaques that coincided with an increase in the number of activated CD16+ monocyte/macrophages and T cells expressing the cognate receptor CCR2. Expression of Mac387 on monocyte/macrophages further indicated that these cells recently migrated to the liver. The hepatic macrophage and T cell levels strongly correlated with liver SIV DNA levels, and were not associated with the levels of 16S bacterial DNA. Utilizing in situ hybridization, SIV-infected cells were found primarily within portal triads, and were identified as T cells. Microarray analysis identified a strong antiviral transcriptomic signature in the liver during SIV infection. In contrast, macaques treated with cART exhibited lower levels of liver macrophages and had a substantial, but not complete, reduction in their inflammatory profile. In addition, residual SIV DNA and bacteria 16S DNA were detected in the livers during cART, implicating the liver as a site on-going immune activation during antiretroviral therapy. These findings provide mechanistic insights regarding how SIV infection promotes liver inflammation through macrophage recruitment, with implications for in HIV-infected individuals.

Nuclear Receptor SHP: A Critical Regulator of miRNA and lncRNA Expression and Function

Small heterodimer partner (SHP, NR0B2) is identified as a unique orphan nuclear receptor that acts as a transcriptional repressor. SHP plays a crucial role in the control of various physiological processes and in several diseases by regulating the expression of disease-specific genes. Non-coding RNAs (ncRNAs), including long noncoding RNAs (lncRNAs) and microRNAs (miRNAs), are encoded of RNAs that are transcribed but not translated into proteins, which are involved in diverse developmental and cellular processes in eukaryotic organisms. Research during the past decade has identified factors participating in the regulation of ncRNAs biogenesis and function. In this review, we summarize recent findings demonstrating a critical role of SHP as a transcriptional regulator of ncRNAs expression and function.

Pregnane X receptor and constitutive androstane receptor modulate differently CYP3A-mediated metabolism in early- and late-stage cholestasis

AIM

To ascertain whether cholestasis affects the expression of two CYP3A isoforms (CYP3A1 and CYP3A2) and of pregnane X receptor (PXR) and constitutive androstane receptor (CAR).

METHODS

Cholestasis was induced by bile duct ligation in 16 male Wistar rats; whereas 8 sham-operated rats were used as controls. Severity of cholestasis was assessed on histological examination of liver sections, and serum concentrations of albumin, AST, ALT, GGT, ALPK and bilirubin. Gene and protein expressions of PXR, CAR, CYP3A1 and CYP3A2 were assessed by means of qRT-PCR and Western blot, respectively. Alterations in CYP3A activity were measured by calculating the kinetic parameters of 4-OH and 1’-OH-midazolam hydroxylation, marker reactions for CYP3A enzymes.

RESULTS

The mRNA and protein expression of CYP3A1 increased significantly in mild cholestasis (P < 0.01). At variance, mRNA and protein expression of CYP3A2 didn’t change in mild cholestasis, whereas the expression and activity of both CYP3A1 and CYP3A2 decreased dramatically when cholestasis became severe. Consistently with these observations, the nuclear expression of both PXR and CAR, which was measured because they both translocate into the cell nucleus after their activation, virtually disappeared in the late stage of cholestatic injury, after an initial increase. These results indicate that early- and late-stage cholestasis affects CYP3A-mediated drug metabolism differently, probably as consequence of the different activation of PXR and CAR.

CONCLUSION

Early- and late-stage cholestasis affects CYP3A-mediated drug metabolism differently. PXR and CAR might be targeted therapeutically to promote CYP3A-mediated liver detoxification.

H19 promotes cholestatic liver fibrosis by preventing ZEB1-mediated inhibition of epithelial cell adhesion molecule

Based on our recent finding that disruption of bile acid (BA) homeostasis in mice results in the induction of hepatic long noncoding RNA H19 expression, we sought to elucidate the role of H19 in cholestatic liver fibrosis. Hepatic overexpression of H19RNA augmented bile duct ligation (BDL)-induced liver fibrosis, which was accompanied by the elevation of serum alanine aminotransferase, aspartate aminotransferase, bilirubin, and BA levels. Multiple genes related to liver fibrosis, inflammation, and biliary hyperplasia were increased in H19-BDL versus null-BDL mice, whereas genes in BA synthesis were decreased. Livers and spleens of H19-BDL mice showed significant enrichment of CD3+γδ+, interleukin-4, and interleukin-17 producing CD4+ and CD8+ immune cell populations. H19 down-regulated hepatic zinc finger E-box-binding homeobox 1 (ZEB1) but up-regulated epithelial cell adhesion molecule (EpCAM) and SRY (sex determining region Y)-box 9 expression. Mechanistically, ZEB1 repressed EpCAM promoter activity and gene transcription. H19RNA impeded ZEB1's inhibitory action by interacting with ZEB1 protein to prevent its binding to the EpCAM promoter. Hepatic overexpression of ZEB1 or knockdown of EpCAM diminished H19-induced fibrosis; the latter was also prevented in H19^-/- mice. H19RNA was markedly induced by bile acids in mouse small cholangiocytes and to a lesser extent in mouse large cholangiocytes. The up-regulation of H19RNA and EpCAM correlated positively with the down-regulation of ZEB1 in primary sclerosing cholangitis and primary biliary cirrhosis liver specimens.

CONCLUSION

The activation of hepatic H19RNA promoted cholestatic liver fibrosis in mice through the ZEB1/EpCAM signaling pathway. (Hepatology 2017;66:1183-1196).

Long Non-coding RNA in Liver Metabolism and Disease: Current Status

Long non-coding RNAs (lncRNAs) are comprised of RNA transcripts exceeding 200 nucleotides in length but lacking identifiable open reading frames (with rare exceptions). Herein, we highlight emerging evidence demonstrating that lncRNAs are critical regulators of liver metabolic function and diseases. We summarize current knowledges about dysregulated lncRNAs and outline the underlying molecular mechanisms by which lncRNAs control hepatic lipid ad glucose metabolism, as well as cholestatic liver disease. lncLSTR, Lnc18q22.2, SRA, HULC, MALAT1, lncLGR, MEG3, and H19, lncHR1, lnc-HC, APOA1-AS, DYNLRB2-2, and LeXis are included in the discussion.

High-mobility-group protein 2 regulated by microRNA-127 and small heterodimer partner modulates pluripotency of mouse embryonic stem cells and liver tumor initiating cells

High‐mobility‐group protein 2 (HMGB2) expression is up‐regulated in human liver cancer; however, little is known about its regulatory function. Here, we establish HMGB2 as a new modulator of the pluripotency of mouse embryonic stem cells. Similar to octamer‐binding transcription factor 4 (OCT4) and sex‐determining region Y‐box 2 (SOX2), HMGB2 protein is highly expressed in undifferentiated CGR8 cells, whereas it undergoes rapid decline during embryonic body formation. HMGB2 interacts with OCT4, increases protein expression of OCT4 and SOX2, and enhances their transcriptional activities. We also show that microRNA (miRNA)‐127 is a translational repressor of HMGB2 protein expression by targeting its 3′ untranslated region. We further elucidate a transcriptional mechanism controlling HMGB2 messenger RNA expression by the nuclear receptor small heterodimer partner (SHP) and transcription factor E2F1. Diminishing HMGB2 expression by ectopic expression of miR‐127 or SHP or treatment with the small molecule inhibitor inflachromene decreases OCT4 and SOX2 expression and facilitates CGR8 differentiation. In addition, HMGB2 is markedly induced in liver tumor initiating cells. Diminishing HMGB2 expression by short hairpin RNA for HMGB2 (shHMGB2), miR‐127, or SHP impairs spheroid formation. Importantly, HMGB2 expression is elevated in various human cancers. Conclusion: HMGB2 acts upstream of OCT4/SOX2 signaling to control embryonic stem cell pluripotency. Diminishing HMGB2 expression by miR‐127 or SHP may provide a potential means to decrease the pluripotency of tumor initiating cells. (Hepatology Communications 2017;1:816–830)

Transient receptor potential canonical 5 channels plays an essential role in hepatic dyslipidemia associated with cholestasis

Transient receptor potential canonical 5 (TRPC5), a calcium-permeable, non-selective cation channel is expressed in the periphery, but there is limited knowledge of its regulatory roles in vivo. Endogenous modulators of TRPC5 include a range of phospholipids that have an established role in liver disease, including lysophosphatidylcholine (LPC). Cholestasis is characterized by impairment of excretion of bile acids, leading to elevation of hepatic bile acids. We investigated the contribution of TRPC5 in a murine model of cholestasis. Wild-type (WT) and TRPC5 knock-out (KO) mice were fed a diet supplemented with 0.5% cholic acid (CA) for 21 days. CA-diet supplementation resulted in enlargement of the liver in WT mice, which was ameliorated in TRPC5 KO mice. Hepatic bile acid and lipid content was elevated in WT mice, with a reduction observed in TRPC5 KO mice. Consistently, liver enzymes were significantly increased in cholestatic WT mice and significantly blunted in TRPC5 KO mice. Localized dyslipidaemia, secondary to cholestasis, was investigated utilizing a selected lipid analysis. This revealed significant perturbations in the lipid profile following CA-diet feeding, with increased cholesterol, triglycerides and phospholipids, in WT, but not TRPC5 KO mice. Our results suggest that activation of TRPC5 contributes to the development of cholestasis and associated dyslipidemia. Modulation of TRPC5 activity may present as a novel therapeutic target for liver disease.

Pyruvate Dehydrogenase Kinase 4 Deficiency Results in Expedited Cellular Proliferation through E2F1-Mediated Increase of Cyclins

Hepatocellular carcinoma (HCC) is a common form of cancer with prevalence worldwide. There are many factors that lead to the development and progression of HCC. This study aimed to identify potential new tumor suppressors, examine their function as cell cycle modulators, and investigate their impact on the cyclin family of proteins and cyclin-dependent kinases (CDKs). In this study, the pyruvate dehydrogenase kinase (PDK)4 gene was shown to have potential tumor suppressor characteristics. PDK4 expression was significantly downregulated in human HCC. Pdk4-/- mouse liver exhibited a consistent increase in cell cycle regulator proteins, including cyclin D1, cyclin E1, cyclin A2, some associated CDKs, and transcription factor E2F1. PDK4-knockdown HCC cells also progressed faster through the cell cycle, which concurrently expressed high levels of cyclins and E2F1 as seen in the Pdk4-/- mice. Interestingly, the induced cyclin E1 and cyclin A2 caused by Pdk4 deficiency was repressed by arsenic treatment in mouse liver and in HCC cells. E2f1 deficiency in E2f1-/- mouse liver or knockdown E2F1 using small hairpin RNAs in HCC cells significantly decreased cyclin E1, cyclin A2, and E2F1 proteins. In contrast, inhibition of PDK4 activity in HCC cells increased cyclin E1, cyclin A2, and E2F1 proteins. These findings demonstrate that PDK4 is a critical regulator of hepatocyte proliferation via E2F1-mediated regulation of cyclins.

Long noncoding RNA MEG3 induces cholestatic liver injury by interaction with PTBP1 to facilitate shp mRNA decay

Bile acids (BAs) play critical physiological functions in cholesterol homeostasis, and deregulation of BA metabolism causes cholestatic liver injury. The long noncoding RNA maternally expressed gene 3 (MEG3) was recently shown as a potential tumor suppressor; however, its basic hepatic function remains elusive. Using RNA pull-down with biotin-labeled sense or anti-sense MEG 3RNA followed by mass spectrometry, we identified RNA-binding protein polypyrimidine tract-binding protein 1 (PTBP1) as a MEG3 interacting protein and validated their interaction by RNA immunoprecipitation (RIP). Bioinformatics analysis revealed putative binding sites for PTBP1 within the coding region (CDS) of small heterodimer partner (SHP), a key repressor of BA biosynthesis. Forced expression of MEG3 in hepatocellular carcinoma cells guided and facilitated PTBP1 binding to the Shp CDS, resulting in Shp mRNA decay. Transient overexpression of MEG3 RNA in vivo in mouse liver caused rapid Shp mRNA degradation and cholestatic liver injury, which was accompanied by the disruption of BA homeostasis, elevation of liver enzymes, as well as dysregulation of BA synthetic enzymes and metabolic genes. Interestingly, RNA sequencing coupled with quantitative PCR (qPCR) revealed a drastic induction of MEG3 RNA in Shp^-/- liver. SHP inhibited MEG3 gene transcription by repressing cAMP response element-binding protein (CREB) transactivation of the MEG3 promoter. In addition, the expression of MEG3 and PTBP1 was activated in human fibrotic and cirrhotic livers.

CONCLUSION

MEG3 causes cholestasis by serving as a guide RNA scaffold to recruit PTBP1 to destabilize Shp mRNA. SHP in turn represses CREB-mediated activation of MEG3 expression in a feedback-regulatory fashion. (Hepatology 2017;65:604-615).

Metabolomics Analysis Revealed Distinct Cyclic Changes of Metabolites Altered by Chronic Ethanol-Plus-Binge and Shp Deficiency

BACKGROUND

Chronic ethanol (EtOH) consumption causes alcoholic liver disease (ALD), and disruption of the circadian system facilitates the development of ALD. Small heterodimer partner (SHP) is a nuclear receptor and critical regulator of hepatic lipid metabolism. This study aimed at depicting circadian metabolomes altered by chronic EtOH-plus-binge and Shp deficiency using high-throughput metabolomics.

METHODS

Wild-type (WT) C57BL/6 and Shp^-/- mice were fed the control diet (CD) or Lieber-DeCarli EtOH liquid diet (ED) for 10 days followed by a single bout of maltose (CD + M) or EtOH (ED + E) binge on the 11th day. Serum and liver were collected over a 24-hour light/dark (LD) cycle at Zeitgeber time ZT12, ZT18, ZT0, and ZT6, and metabolomics was performed using gas chromatography-mass spectrometry.

RESULTS

A total of 110 metabolites were identified in liver and of those 80 were also present in serum from pathways of carbohydrates, lipids, pentose phosphate, amino acids, nucleotides, and tricarboxylic acid cycle. In the liver, 91% of metabolites displayed rhythmicity with ED + E, whereas in the serum, only 87% were rhythmic. Bioinformatics analysis identified unique metabolome patterns altered in WT CD + M, WT ED + E, Shp^-/- CD + M, and Shp^-/- ED + E groups. Specifically, metabolites from the nucleotide and amino acid pathway (ribose, glucose-6-phosphate, glutamic acid, aspartic acid, and sedoheptulose-7-P) were elevated in Shp^-/- CD + M mice during the dark cycle, whereas metabolites including N-methylalanine, 2-hydroxybutyric acid, and 2-hydroxyglutarate were elevated in WT ED + E mice during the light cycle. The rhythmicity and abundance of other individual metabolites were also significantly altered by both control and EtOH diets.

CONCLUSIONS

Metabolomics provides a useful means to identify unique metabolites altered by chronic EtOH-plus-binge.

REV-ERBα Activates C/EBP Homologous Protein to Control Small Heterodimer Partner-Mediated Oscillation of Alcoholic Fatty Liver

The small heterodimer partner (SHP) nuclear receptor is an important regulator of nonalcoholic fatty liver disease. However, little is known about the role of SHP in alcoholic fatty liver. In this study, we used a modified chronic ethanol-binge model to examine cyclic alterations of lipid metabolism in wild-type (WT) and Shp^-/- mice over a 24-hour period after binge. The serum and hepatic lipid profiles, as well as the expression of lipid synthesis genes and markers of endoplasmic reticulum stress, exhibited distinct variations in WT and Shp^-/- mice in response to ethanol diet plus ethanol binge (ED+E) and control diet plus maltose binge. ED+E induced steatosis in WT mice, which correlated with a marked up-regulation of activating transcription factor 4 protein (ATF4) but down-regulation of C/EBP homologous protein (CHOP) and sterol regulatory element-binding transcription factor 1c protein (SREBP-1c). On the contrary, the control diet plus maltose binge caused lipid accumulation in Shp^-/- mice, which was accompanied by a sharp elevation of CHOP, SREBP-1c, and REV-ERBα proteins but a diminished ATF4. REV-ERBα activated CHOP promoter activity and gene transcription, which were inhibited by SHP. Knockdown Rev-Erbα in Shp^-/- mice prevented steatosis induced by ED+E. Our study revealed a critical role of SHP and REV-ERBα in controlling rhythmic CHOP expression in alcoholic fatty liver.

A Novel Small Molecule Activator of Nuclear Receptor SHP Inhibits HCC Cell Migration via Suppressing Ccl2

Small heterodimer partner (SHP, NR0B2) is a nuclear orphan receptor without endogenous ligands. Due to its crucial inhibitory role in liver cancer, it is of importance to identify small molecule agonists of SHP. As such, we initiated a probe discovery effort to identify compounds capable of modulating SHP function. First, we performed binding assays using small molecule microarrays (SMM) and discovered 5-(diethylsulfamoyl)-3-hydroxynaphthalene-2-carboxylic acid (DSHN) as a novel activator of SHP. DSHN transcriptionally activated Shp mRNA, but also stabilized the SHP protein by preventing its ubiquitination and degradation. Second, we identified Ccl2 as a new SHP target gene by RNA-seq. We showed that activation of SHP by DSHN repressed Ccl2 expression and secretion by inhibiting p65 activation of CCL2 promoter activity, as demonstrated in vivo in Shp^-/- mice and in vitro in HCC cells with SHP overexpression and knockdown. Third, we elucidated a strong inhibitory effect of SHP and DSHN on HCC cell migration and invasion by antagonizing the effect of CCL2. Lastly, by interrogating a publicly available database to retrieve SHP expression profiles from multiple types of human cancers, we established a negative association of SHP expression with human cancer metastasis and patient survival. In summary, the discovery of a novel small molecule activator of SHP provides a therapeutic perspective for future translational and preclinical studies to inhibit HCC metastasis by blocking Ccl2 signaling. Mol Cancer Ther; 15(10); 2294-301. ©2016 AACR.

Circadian clock control of hepatic lipid metabolism: role of small heterodimer partner (Shp)

Hepatic steatosis, the accumulation of triglyceride droplets in the hepatocytes, is a common hepatic pathology seen in subjects with obesity/metabolic syndrome and those with excessive alcohol use. The pathogenesis underlying hepatic steatosis is complex. Recent studies have shown the specific role played by the molecular clock mechanism in the control of lipid metabolism and that the disruption of these tissue clocks may lead to the disturbances in lipid homeostasis. This review reports a novel role of small heterodimer partner in maintaining triglyceride and lipoprotein homeostasis through neuronal PAS domain protein 2.